The present invention relates to the tread of a tire intended to travel on sand or sandy soils, that is to say, soils formed of a mixture of sand and another material in small proportion.
The tread of such a tire is generally formed of blocks of rubber separated from each other in the axial direction of the tire by linear or broken-line longitudinal grooves and/or, in the longitudinal direction of the tire, by transverse grooves which debouch on the edges of the tread. These blocks of rubber are of such a nature that in the contact surface between the tire and hard flat ground they occupy an area of between 40% and 60% of the total area of the contact surface, the tire being mounted on its normal operating rim, bearing the recommended normal load, and being inflated to the corresponding normal pressure recommended for travel on sand.
It is obvious that the conditions of travel recommended for tires of the type in question in the case of travel on sandy tracks or on pure sand are different from the conditions recommended in the case of highway travel: for a given load, it is known that the inflation pressure is lowered, the decrease in inflation pressure possibly amounting to 50% and more of the pressure recommended for highway travel.
Despite this, there are still numerous difficulties encountered by vehicles equipped with such tires when they are confronted by layers of sand of substantial thickness.